Sites like HalfBakery and this shared Google Doc act as open repositories for potentially patentable inventions. In effect, these sites act as anti-patent databases because the inventions are never pursued, but are available as prior art in the public domain. Is there currently a site or service that aggregates all of these different open repositories into one location?

Don't know of a centralized database. Yet another resource is IP.com. They have have a defensive publication service. You have to pay to publish there, but you'll have the benefit of a more trustworthy documentation system.